Applicant claims priority under 35 U.S.C. xc2xa7119 of German Application No. 197 50 493.0 filed Nov. 14, 1997. Applicant also claims priority under 35 U.S.C. xc2xa7120 of PCT/DE98/03303 filed on Nov. 5, 1998. The international application under PCT article 21 (2) was not published in English.
The invention concerns an implant for stabilization of a fracture of the humerus in the area of the head of the humerus with or without cooperation of the tubercula with a plate, in which holes for screws are provided, thus the plate provides a guide for a humerus head screw, which holds the humerus head screw in a stable way at an angle against the plate.
As a generic implant a disk for underlying and guiding is known from U.S. Pat. No. 5,693,055, which receives the forces at the screw head and by means of an increased contact surface on the shaft bone of the humerus achieves a reduced stress in the bone shaft. This guiding plate lies on the shaft bone rather like a washer disk and is fixed against the shaft bone only by the screw inserted into the humerus head. The function of the implant described in U.S. Pat. No. 5,693,055 consequently relies on the force of the screw in the humerus head and thus the inter-fragmentary compression generated, which, however, as experience shows, slackens within hours to days due to regularly occurring bone sintering.
A different implant is known from U.S. Pat. No. 4,657,001. This implant, however, is only suitable for the upper leg area and also leads to an inter-fragmentary compression.
The invention is therefore based on the task of further developing a generic implant, so that an easy, safe stabilization of the fracture can be achieved with it.
This task is solved by the plate providing a clamping device, which attaches the humerus head screws in a stable way against a shift in shaft direction and which is preferably removable. Such a clamping device blocks movements of the screw relative to the plate and consequently provides for an implant which holds rigidly, that cannot loosen even under strong movements of the upper arm.
When using two humerus head screws, not only is an angle-stable fixation of the head and shaft fragment of the bone against each other ensured, but also a rotation stability is achieved which prevents the loosening of the humerus head screws, e.g. during swinging excercises.
nAn application example provides, that the guides are part of the holes, the cross-sections of which correspond to a barrel diameter of the humerus head screws. These guides use the thickness of the plate, to hold the screws at an angle. To do this, the inner diameter of the hole is adjusted on at least one section of the hole exactly to the outer diameter of a barrel section of the screw, so that the screw can be inserted into the hole, but after this, can only be moved in the direction of the axis of the screw barrel. Although this configuration requires a certain thickness of the plate, it is, however, preferable for guides that project above the plate surface or to the contrary reach into the bone.
The angle pre-defined by the guides should approximately correspond with the angle of the humerus head. Therefore, an angle between 35xc2x0 and 40xc2x0 preferably 37.5xc2x0 is proposed, measured against the longitudinal axis of the humerus shaft.
A preferred configuration of such a clamping device provides, that a gap with a cross hole is provided between the holes of the humerus head screws. A screw can be inserted into this cross hole in such a way that the gap is narrowed by tightening the screw. This causes the diameter of the holes to be slightly deformed and therefore to attach the humerus screws under retention of their angular position.
Preferably, the holes of the humerus head screws are arranged parallel to each other, so that their axes are in a single plane with the longitudinal axis of the humerus shaft. The axes of the humerus head screws consequently cross the longitudinal axis of the humerus shaft in the pre-defined angle at preferably 35xc2x0-40xc2x0. This arrangement of the screws on one line enables an operation with a very narrow exposure of the bone in the fractured area. This leads to a fast bone healing, because disturbances of the blood circulation are avoided.
To implement wire cerelages or PDS cords for re-attachment of a torn out tubercula, it is proposed to add holes on the plate running parallel to its upper and lower sides. These holes are to be preferably provided at the tip of the plate and in the area of the clamping device.
A preferred configuration of the plate is designed in a very compact way. This plate has a maximum length of 100 mm, a maximum width of 12 mm and its thickness is between 4 mm and 9.5 mm. A special design of the screw guide allows a maximum plate thickness of approximately 7 mm. In its shape the plate is adjusted to the anatomic conditions in the area of the proximal humerus. In the lower section the plate it is screwed with standard Corticalis screws at the proximal part of the humerus shaft. Due to the fact that in this area close to the joint no high bending moments occur, an attachment with three screws is sufficient. To cater for fractures, which reach into the humerus shaft area, the plate can also be designed longer with a correspondingly higher number of screw holes in the area of the humerus shaft.